In conventional High Speed Packet Access (HSPA) networks, mobile usage in e.g. stadiums and at special events are characterized by strong bandwidth requirement in the Uplink (UL) as users often undertake photo and video uploads to applications, such as Facebook and YouTube. Often the communication network experiences excessive received power in this type of scenarios known as power rises and the resulting user experience is therefore poor.
Inter-cell interference is the main cause of the above mentioned problem. Cloud Radio Access Network (RAN) architectures in which received signal processing from many cells of a network is processed centrally in a single network node can address this issue by combining the received signals at multiple cell sites arising from a single UL transmission from a user. However, it is not always practical or cost-effective to deploy a Cloud RAN since e.g. very fast backhaul (such as fibre backhaul) must be provided between each cell site and the central baseband processing unit.
The most important characteristics of the network structure and the data and control channels over the air interface for High Speed Uplink Packet Access (HSUPA) are:                A User Equipment (UE) transmits user plane data on the E-DPDCH channel when granted radio resources by its serving cell;        Grants control the transmission rate the UE can transmit (equivalently the transmit power or modulation and coding scheme):                    The serving cell issues “absolute grants” indicating a baseline rate,            “Relative grants” issued by all cells in the active set (see below) can then adjust this up or down (or stay the same, “hold”),            Grant decisions and scheduling decisions are made in the Node Bs.                        For cell edge UEs these transmissions may be decoded at multiple cells (the set of cells is called the active set) this is known as soft handover and improves the throughput of the UE:                    Typically add links to active set when within a threshold (e.g. 3 dB) of the serving cell in DL strength (Received Signal Code Power, RSCP),            Typically active set size is limited to two or four.                        A Node B can support multiple cells that are part of the active set of a UE—these cells are called the Radio Link Set (RLS):                    Transmissions over a RLS can be soft combined at the Node B—this is called softer handover.                        Each RLS uses a Hybrid Automatic Repeat Request (HARQ) protocol to manage retransmissions and combination of transmissions of the same packet by the UE:                    The UE will continue to retransmit a packet until one RLS indicates it has been received successfully (with a HARQ Acknowledgement (ACK)).                        All successfully received packets are sent over the so called Iub interface to the Radio Network Controller (RNC) which performs reordering if they are out-of-sequence.        
In typical HSUPA implementations the Downlink (DL) control signalling on active set legs consumes significant power especially the Downlink Physical Control Channel (DPCCH) channel. Further, the DL and UL path losses are often not balanced for a UE to a cell because HSUPA use Frequency Division Duplex (FDD), so the UL radio links with the lowest losses are not identified by the DL RSCP measurement performed by the UE, and are therefore not included in the active set. The limitation of the active set size means useful power on the UL is not demodulated meaning higher UE transmit power and greater inter-cell interference.
One conventional solution uses a technique in which DL active sets and UL active sets are no longer matched which means that more links are used in the UL than in the DL. Further, active set on the uplink is extended for Node Bs which have an existing UL radio link. This solution needs to have an existing DL radio link for that Node B. Also UL signal combining only occurs for links of a single Node B.
The limitations of this method are that the method is unable to add links on uplink unless recognized that there should be a downlink radio link from same Node B. Further, the method does not address DL/UL imbalance and also limits combining gain on the UL. Also this method does not reduce overhead of DL control channels.
Another conventional solution is called Cooperative Multipoint Transmission/Reception (COMP) and is a set of schemes introduced for LTE Advanced which exploit coordination of transmissions to/from multiple base stations (eNBs). On the uplink, COMP may combine the received signals from a UE at two different base stations together at one of the two base stations. This is similar to soft combining (softer handoff) in HSUPA but occurs using two base stations at different locations. Alternatively, interference may be cancelled at one base station using the received signal from the same UE transmission at another base station. Both methods require a high bandwidth and low delay backhaul interface between base stations to exchange received signals (e.g. received soft bits after demodulation). The bandwidth of the backhaul needs to be high to exchange the volume of bits (hard or soft) for each transmission (every TTI which is 1 ms for LTE), and delay must be low such that the HARQ ACK/NACK can be generated in a timely fashion (4 ms). This backhaul is typically fibre, which is very expensive to install. COMP can also exploit a third node in a more hierarchical configuration—this is often called CloudRAN.
For HSUPA, COMP could be realized with joint combining at the RNC or other central node if fibre backhaul was provided. For HSUPA the TTI is typically 2 ms and the time before a NACK/ACK should be sent is about 6 ms.
Thus, there is a need for improved solutions in the art.